The brake calipers are usually fixedly connected to a support structure or hub bracket that stays immobile with respect to the disc, like for example a structure for discharging the braking action to the stub axle of a vehicle's suspension.
In a typical arrangement, one of the two elongated elements of the fixed caliper body has attachment portions of the body of the caliper to the support structure, for example foreseeing slots or eyelets, for example arranged axially, or through holes, for example arranged radially, suitable for receiving screws or stud bolts for fixing the caliper that, with their ends are received in threaded holes foreseen on the support of the caliper.
In a typical caliper body construction, the elongated elements arranged facing the braking surfaces of the disc are connected together by bridge elements arranged astride of the disc.
The caliper comprises various components mounted on the body such as pistons, gaskets, drainage devices and brake fluid supply ducts.
Typically, the body of the caliper is made from metal like for example aluminium, or aluminium alloy, for example aluminium and lithium or steel. The body of the caliper can be obtained by casting, but also by mechanical chip removal machining, as well as by forging.
The body of the caliper can be produced both in a single piece or monoblock, and also in two half-calipers typically connected together along a plane that usually coincides with the middle plane of the disc on which the caliper is arranged astride.
In the case in which the driver of the vehicle wishes to brake or slow down the speed of the vehicle, he applies a pressure on the brake pedal. Such pressure on the brake pedal, by means of a brake pump, exerts a pressure on the brake fluid that, through a duct, applies on the brake fluid present in the hydraulic circuit arranged inside the body of the caliper until it reaches the cylinders where the pressure is exerted on the bottom surface of the pistons, forcing them to clamp against the pads, which in turn abut against the braking surfaces of the disc.
The pressure action of the brake fluid is also exerted on the bottom wall of the cylinder causing a reaction in the body of the caliper that deforms it away from the surfaces of the disc and, due to the constraint between the caliper and its support arranged only on the side of the caliper of the hub-side elongated element, a shearing deformation and torsion that makes the elongated element not constrained to the support or wheel-side elongated element move with respect to the hub-side elongated element, bending the connection bridges between these elongated elements. The body of the caliper also deforms as a function of the torque exerted by the action of the pistons that abut the pads against the braking surfaces of the disc applied in directions that form torque arms with respect to the attachment points of the caliper body to its support. These torques also deform the caliper body in the tangential and radial direction with respect to the disc, as well as in the axial direction. This deformation of the body of the caliper leads to an increase in the stroke of the pistons and therefore to an increase in the stroke of the brake pedal.
The caliper body must therefore have a sufficient structural rigidity, so as to ensure that this deformation of the body of the caliper caused by the braking action is kept within tolerable values, which as well as avoiding damage to the braking system do not create the sensation for the driver of an unresponsive braking system, determining an extra stroke of the lever or pedal of the braking system creating a feeling of a spongy system. This requirement pushes towards having extremely rigid structures for the bodies of the calipers and therefore towards increasing their bulk and weight, in applications where this is possible.
On the other hand, since the body of the caliper is fixedly connected to the vehicle's suspension and is arranged astride of the disc, it is one of the unsuspended masses that it is wished to reduce as much as possible or to keep the weight constant whilst increasing the performance, also in braking, of the vehicle.
Of course, these considerations are taken to the extreme when the vehicle is for racing and the user wishes to have a braking system that is extremely responsive to his commands and at the same time extremely light so as not to penalize the performance of the racing vehicle.
Therefore, there is a great need for an assembly of a caliper for a disc brake and its support or hub bracket that has improved structural characteristics for the same weight of the body of the caliper, or else having a lower weight with respect to solutions of the prior art for the same structural characteristics.
Solutions for caliper bodies are known that a specially studied to increase the characteristics of structural rigidity. For example European patent application EP-A-2022999, European patent application EP-A-153497, U.S. Pat. No. 6,708,802, European patent application EP-A-1911989, international patent application PCT/EP2005/050615, Japanese patent applications JP-A-09257063 and JP-A-2000/337408, American patent application US 2010/0012443 and U.S. Pat. No. 3,183,999 all present solutions of bodies for brake calipers equipped with reinforcement elements, for example arranged around the caliper bodies or between the caliper body and its support. In some of these known solutions the caliper body is of the type that is symmetrical according to planes passing through the axis of the disc or through the middle of the disc. In other solutions the caliper body has large and distributed windows also passing right through that form elongated reinforcement elements arranged longitudinally to the body of the caliper.
These known solutions, however, do not make it possible to obtain assemblies of a caliper and its support that maximise the structural rigidity of the body of the caliper while keeping the weights unaltered and at the same time are capable of keeping to bulk as low as possible so as to facilitate the mounting of the body of the caliper also inside a rim and wheel on which brake discs having a large diameter are mounted.
Document JP 2007-032719-A to ADVICS KK shows a brake caliper for a motor vehicle formed in one piece with a main caliper body that extends from the fork of the motor vehicle arranged at the side of the wheel and of the brake disc. Outer portions of caliper body are connected to the fork.
However, this known solution cannot be applied to an automobile that, unlike a motor vehicle, has the wheel arranged on the outer side of the vehicle and forces the provision of a support or hub bracket to connect the caliper to the suspension through a bearing. In other words, the fork of the motor vehicle is arranged substantially coplanar to the caliper body and can be easily connected to it. Moreover, in a motor vehicle there are not restrictions as to the bulk of the connections of the caliper to the fork, whereas in an automobile the entire braking system must be substantially housed inside the rim of the wheel, preventing easy connection of the caliper body to its support. Moreover, this known solution foresees the connection of the caliper body to the fork through attachments with axial pins or connections with radial screws, being not very effective in counteracting the deformation of the caliper body when stressed by the braking action.